Server load balancing (SLB) is a key service provided in many conventional data centers today. This load balancing can be performed at any layer of OSI model (Open Systems Interconnection Basic Reference Model) from layer 3 to layer 7, depending on the particular application hosted on the server.
Other devices can be load balanced by content switches, such as firewalls, Web application or database servers, virtual private network (VPN) concentrators, caches, and secure sockets layer (SSL) offload devices. An SLB device may “virtualize” a group of servers, and load balance user requests to that virtual group. Typically, a user request may get classified, a server may be selected, network address translation (NAT) can occur, and then the request can be sent to the server.